PID and Cooling Water Pump Control

[deep6ixed]

Time to reach out and ask for some help from the Do-More users.  I'm using a BRX to run our brand spankin' new cooling pump controller for our mesh welder and I'm not sure if I'm using it in the most optimal way.

Here's what we want:  When the machine runs it generates heat due to welding and the return temp from the machine goes up.  We want the cooling pump to speed up and supply more water to lower the temp back down to the supply temp.  As the machine sits idle it cools back off and the pump slows down.

I've set the PID SP to the current cooling water temp from our cooling tower and the PV is the machine return temp, and then Clamp the PID output to be between 20-60hz motor speed.  Anything slower and the pump cavitates and makes noise, and we need to have water flowing to see a temp change. 

Does anyone here have any experience doing something like this?

[ADC Product Engineer]

Setting your SP to the value of your incoming water won't work.  Your PID will never stabilize. 

It needs to be set at a some positive offset that correlates to an optimum temperature that the welder is happy with and is achievable by the cooler at max load.  IE inlet is 70 degrees, setpoint might be 150 degrees. 

[deep6ixed]

We use a cooling tower and our cooling capacity varies based on the outside temp.  So in the summer, the cooling water might be 90 but in the winter it can be as cold as 50%

I was looking at setting the SP to a desired flow rate, and then setting the desired flow rate based on machine temp.  Once the machine cools off, and the temp matches the incoming temp, back the flow off to a preset holding flow.  Might not even need a PID loop. 

[Garyhlucas]

Set the PID setpoint at the desired return temperature that makes the welder happy and it should work fine.  Have you tried autotune on the PID loop?  Do-More autotune is awesome!  It took five seconds to tune our blowers, about 10 seconds each for the 3 centrifugal pumps, and 45 minutes for the pH loop that has a big lag.  They all run beautifully, way better than any manual tuning I have ever done.  Once you get over the fear of PID tuning you might find that the system will work better with multiple PID loops tuned for the outside temperature ranges.  We did that for our blowers based on how many are running.